The goal of this research is to determine the intermolecular interactions that stabilize the polymeric structure of deoxygenated sickle cell hemoglobin. With this information it may be possible to find a means of disrupting or preventing the aggregation which is responsible for the sickling of erythrocytes. Investigations are by methods of X-ray diffraction. Since fiber patterns are inherently of low resolution caused by cylindrical averaging, a model system for the fiber that can yeild high resolution diffraction data is sought. Such a structure has been found in which needle-like crystals grow at the expense of fibers and give rise to a rotation diagram that is strikingly similar to that of the fiber, with few notable differences. The similarities offer compelling evidence that the building block of the polymer and the crystal is the same. It consists of a pair of filaments in which one filament is displaced parallel to the fiber axis with respect to its neighbor by half a molecular diameter. The number of pairs of filaments in the fiber and how they pack to form the cylindrical structure remains to be determined. Another crystalline form has been found, which also grows at the expense of the fibers and whose diffraction pattern in conjunction with the pattern of the initial crystalline form corresponds more closely to the transform of the fiber. With the determination of the structure of this new crystalline form, the disposition of pairs of filaments within the fiber should emerge.